German Patent Application No. 100 20 041 A1 describes a bypass valve body for turbo gasoline internal combustion engines. A connection between the pressure side and the intake side of a boost pressure pump is established via the bypass valve body. The bypass valve body includes a housing, within which a valve rod is movable with the aid of a drive unit, a valve head having a valve closing element being situated on the valve rod. The valve head and the valve rod each have at least one pressure equalization borehole. An electrically operable drive system is used as the drive unit. The electrically operable drive system is preferably an electromagnetic drive. A diaphragm having a circumferential sealing lip is situated between the housing and the valve head as the valve closing element. A connection between the valve rod and the valve head is designed as a universal spherical joint.
In turbocharged internal combustion engines, measures are generally necessary during rapid negative load changes from the close to full-load range, as they occur when a throttle valve is closed, to avoid separation of the airflow at the compressor wheel of a supercharging device which is designed as an exhaust gas turbocharger, for example. An unacceptable acoustic load, in the extreme case even damage to the compressor wheel or to its axial bearings, would occur without these measures. In order to avoid these effects, a bypass system is opened to the compressor element of the supercharging device in this operating situation which allows the compressor element to reduce the air volume flow without pumping and without major instability, i.e., without flow separation.
In the conventional approach, an electrical drive and a pressure-equalized diaphragm are provided. A coil/armature combination having a plunger module is used as the electrical drive. A diaphragm is connected to the armature of the electrical drive which divides a flow path using a sealing geometry. Since an overpressure up to 2 bar may occur on one side, the diaphragm has an essentially pressure-equalized design. The space underneath the diaphragm is short-circuited with the space upstream from the sealing geometry which results in the diaphragm being able to be operated with only little magnetic force—generated by the coil of the electrical drive. This has the advantage that the electrical drive may be designed having relatively small dimensions.
Since the conventional system may be attached to a supercharging device designed as an exhaust gas turbocharger, for example, the electrical drive as well as the moved mass must be designed for accelerations of up to 40 g. To ensure the sealing fit of the diaphragm during an excitation from the outside, the diaphragm is set into the sealing seat using a spring. When the diaphragm is operated, it carries out a lift of a few millimeters. In order to achieve this, the diaphragm is designed as a rolling diaphragm having a bead.
This approach has the disadvantage that the diaphragm is designed as a rolling diaphragm. Due to its assembled position on an internal combustion engine, the rolling diaphragm is exposed to very high temperatures and must therefore be manufactured using a very high-grade elastomer material. On the one hand, the elastomer material must be resistant to fuel and other media in the engine compartment and, on the other hand, it must be resistant in a temperature range between −40° C. and +160° C. Moreover, the diaphragm is exposed to approximately 1.5 million load cycles during its service life. This places very high demands on the churning behavior of such a diaphragm designed as a rolling diaphragm. The churning behavior of a diaphragm depends on the long-term characteristics of the elastomer material used which, due to its use conditions, in particular the temperature and the number of executed load cycles, continuously subsides over the diaphragm's service life, which, in the extreme case of depleted elastic characteristics of the diaphragm material, may result in the diaphragm's failure.